Looks to me like all it does is change your network settings form half duplex to full duplex. That's something anybody can do. Go look up "Leatrix Latency Fix" on google. It's on a WoW forum but it works with any game.

We're not going to be able to give you the "OK" on any third party app as far as it being "safe" for use in Diablo III. However, as long as it doesn't modify any of our game files, it's generally going to be fine. There are exceptions but this particular app and what it currently does shouldn't cause any account issues. Of course, since it's not supported, should you encounter any problems, you'd need to uninstall it before asking for help.